摘要
【目的】探究梯度热解过程中竹材灰分质量分数变化及组成转化规律,重点探讨硅元素在竹材不同部位的分布特点,揭示高温热解对硅元素分布的影响机制,为开发高效的竹材脱灰工艺和制备高纯度竹炭提供数据支撑。【方法】选取1年生毛竹,采用SEM-EDXA、XRF、XRD等分析技术,对比研究不同梯度热解时(350、500、800、1000℃)竹材不同部位(竹材内外表皮、气孔、节间、竹节)灰分质量分数变化及组成转化规律,探讨硅元素在竹材内外表皮、气孔、竹青、竹肉、竹黄处的分布特点,阐明高温热解对硅元素分布的影响机制。【结果】竹材灰分主要由CaO、K_(2)O、SiO_(2)、Al_(2)O_(3)等组成,也含有一定量的硫氧化物(SO_(3))、磷氧化物(P_(2)O_(5))。XRD分析表明,节间炭灰分组成为KCl、K_(2)SO_(4)、KalSiO、KFeSiO_(4)等,竹节中除上述无机盐外,还含有明显结晶态的SiO_(2)。当热解温度达800℃时,KAlSiO、KFeSiO_(4)等含硅无机盐类生成,炭基体中出现短程有序的涡轮层状结构。对比节间和竹节硅元素分布发现,二者在外表皮、气孔处均具有极高质量分数的硅;与节间不同,竹节处除临近表皮的薄壁细胞中出现含硅颗粒外,竹肉和竹黄薄壁细胞中也出现微米级含硅颗粒,且均以硅氧化物形式存在。SEM-EDXA元素分布半定量分析表明,节间和竹节硅元素质量分数在500℃达到最高,竹材外表皮硅元素质量分数在800℃达到最高。随着高温条件硅酸盐和硅铝酸盐的生成,硅元素质量分数逐渐降低。钾元素质量分数在整个热解过程中呈线性升高趋势。高温热处理过程中,因氢、氧等元素挥发以及少量碳元素消耗,细胞壁中部分硅裸露出来,形成硅氧化物沉积于导管和薄壁细胞的细胞腔中。【结论】1)节间和竹节中灰分组成近似,节间灰分质量分数更高;硅元素广泛分布于竹材外表皮、气孔以及临近竹青的薄壁细胞中;2)当热解温度达500℃时,竹节和节间中CaO、K_(2)O等无机盐的质量分数达到最大,持续升温至800℃时,这些无机盐类转化为硅酸盐和硅铝酸盐;3)高温热处理造成节间硅的释放,沉积于导管和薄壁细胞的细胞腔中。
【Objective】In the present work,the evolution of ash composition and transformation mechanism was interpreted in details.Importantly,the distribution pattern of silicon in internodes and nodes as well as the effects of gradient pyrolysis on the silicon deposition will be investigated.The above results will provide theoretical and data support for the development of efficient ash removal process as well as the production of high purity bamboo charcoal and bamboo activated carbon.【Method】One-yearold moso bamboo(Phyllostachys edulis)was selected,and SEM-EDXA,XRF,XRD and other analytical techniques were used to study the changing rules of ash content and composition in different parts of bamboo(internodes,nodes,inner bark,outer bark and stomata)under the gradient pyrolysis conditions(350,500,800,and 1000℃).Also,the combination of all these techniques were used to explore the distribution of silicon in the various parts of bamboo(inner and outer bark,stomata,bamboo green,bamboo timber,and bamboo yellow)and the effects of the pyrolysis treatment on the silicon distribution.【Result】The ash of bamboo mainly consisted of CaO,K_(2)O,SiO_(2),Al_(2)O_(3),and certain sulfur oxides(SO_(3))and phosphorus oxides(P_(2)O_(5)).XRD analysis showed that the ash of bamboo internodes was mainly composed of KCl,K_(2)SO_(4),KAlSiO,KFeSiO_(4),etc.In addition to the above inorganic salts,there were obvious crystalline SiO_(2) characteristic peaks in the internodes.Silicon-containing inorganic salts,such as KAlSiO,and KFeSiO_(4)were generated and short-range order of turbostratic stacks in bamboo charcoal occured when the pyrolysis temperature reaches 800℃Higher silicon content was observed in the bark and stomata for both internodes and nodes.Besides the parenchyma near the epidermis containing silicon particles,the parenchyma located in bamboo timber and yellow also existed micrometers silicon oxides.The relative content of silicon reached the maximum at 500℃,while the relative content of silicon began to decrease at 800℃with the generation of silicate and aluminosilicate.The relative content of potassium showed a linear increase throughout the pyrolysis process.High-temperature heat treatment caused the volatilization of elements such as H and O,the consumption of carbon,resulting in the release of silicon which were deposited in the lumen of the vessel and parenchyma.【Conclusion】1)Bamboo nodes and internodes displayed the similar ash composition,while the internode parts had a higher silicon content.Silicon was widely distributed in the bamboo outer bark,stomata and parenchyma adjacent to bamboo green.2)The relative content of CaO and K_(2)O in the nodes and internodes displayed the maximum value when the pyrolysis temperature reached 500℃Increasing the pyrolysis temperature to 800℃converted these inorganic salts into silicate and aluminosilicate.3)High-temperature treatment caused the release of silicon in the internodes,which was deposited in the lumen of vessel and parenchyma.
作者
马欣欣
王游
王佳军
冯龙
马建锋
Ma Xinxin;Wang You;Wang Jiajun;Feng Long;Ma Jianfeng(Key Laboratory of Bamboo&Rattan Science and TechnologyInternational Centre for Bamboo and Rattan,Beijing 100102)
出处
《林业科学》
北大核心
2025年第2期172-179,共8页
Scientia Silvae Sinicae
基金
国际竹藤中心基本业务费项目“竹纤维超分子结构的温度响应机制研究”(1632022017)。
关键词
毛竹
高温热解
竹材灰分组成
硅分布
moso bamboo(Phyllostachys edulis)
high temperature pyrolysis
ash composition of bamboo
silicon distribution
